Metal lithium chloride derivatives in the space group of P21/c as Li super-ionic conductor, solid electrolyte, and coating layer for Li metal battery and Li-ion battery

ABSTRACT

Solid-state lithium ion electrolytes of metal lithium chloride derivative compounds having a crystal morphology in the P21/c space group are provided as materials for conducting lithium ions. An activation energy of the lithium aluminum chloride derivative compounds is from 0.15 to 0.40 eV and conductivities are from 0.01 to 3 mS/cm at 300K. Compounds of specific formulae are provided and methods to alter the materials with inclusion of aliovalent ions shown. Lithium batteries containing the composite lithium ion electrolytes and electrodes containing the lithium aluminum chloride derivative compounds are also provided.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

The disclosure herein is a result of joint research effort conductedunder a joint research agreement between TOYOTA MOTOR ENGINEERING &MANUFACTURING NORTH AMERICA, INC. having an address of 6565 HeadquartersDrive W1-3C, Plano, Tex., 75024, and UNIVERSITY OF MARYLAND, COLLEGEPARK having an address of 2130 Mitchell Bldg. 7999 Regents Dr. CollegePark, Md., 20742.

FIELD OF DISCLOSURE

This disclosure is directed to novel LiCl₄ derivative compounds of highlithium ion conductivity having a crystal structure of the P2₁/c spacegroup which are useful as solid electrolytes and electrode componentsand/or electrode coatings for Li ion and Li metal batteries.

BACKGROUND

Li-ion batteries have traditionally dominated the market of portableelectronic devices. However, conventional Li-ion batteries containflammable organic solvents as components of the electrolyte and thisflammability is the basis of a safety risk which is of concern and couldlimit or prevent the use of Li-ion batteries for application in largescale energy storage.

Replacing the flammable organic liquid electrolyte with a solidLi-conductive phase would alleviate this safety issue, and may provideadditional advantages such as improved mechanical and thermal stability.A primary function of the solid Li-conductive phase, usually calledsolid Li-ion conductor or solid state electrolyte, is to conduct Li⁺ions from the anode side to the cathode side during discharge and fromthe cathode side to the anode side during charge while blocking thedirect transport of electrons between electrodes within the battery.

Moreover, lithium batteries constructed with nonaqueous electrolytes areknown to form dendritic lithium metal structures projecting from theanode to the cathode over repeated discharge and charge cycles. If andwhen such a dendrite structure projects to the cathode and shorts thebattery energy is rapidly released and may initiate ignition of theorganic solvent.

Therefore, there is much interest and effort focused on the discovery ofnew solid Li-ion conducting materials which would lead to an all solidstate lithium battery. Studies in the past decades have focused mainlyon ionically conducting oxides such as for example, LISICON(Li₁₄ZnGe₄O₁₆), NASICON (Li₁₃Al_(0.3) Ti_(1.7)(PO₄)₃), perovskite (forexample, La_(0.5)Li_(0.5)TiO₃), garnet (Li₇La₃Zr₂O₁₂), LiPON (forexample, Li_(2.88)PO_(3.73)N_(0.14)) and sulfides, such as, for example,Li₃PS₄, Li₇P₃S₁₁ and LGPS (Li₁₀GeP₂S₁₂).

While recent developments have marked the conductivity of solid Li-ionconductor to the level of 1-10 mS/cm, which is comparable to that inliquid phase electrolyte, finding new Li-ion solid state conductors isof great interest.

An effective lithium ion solid-state conductor will have a high Li⁺conductivity at room temperature. Generally, the Li⁺ conductivity shouldbe no less than 10⁻⁶ S/cm. Further, the activation energy of Li⁺migration in the conductor must be low for use over a range of operationtemperatures that might be encountered in the environment. Additionally,the material should have good stability against chemical,electrochemical and thermal degradation. Unlike many conventionallyemployed non-aqueous solvents, the solid-state conductor material shouldbe stable to electrochemical degradation reactivity with the anode andcathode chemical composition. The material should have low grainboundary resistance for usage in an all solid-state battery. Ideally,the synthesis of the material should be easy and the cost should not behigh.

The standard redox potential of Li/Li+ is −3.04 V, making lithium metalone of the strongest reducing agens available. Consequently, Li metalcan reduce most known cationic species to a lower oxidation state.Because of this strong reducing capability when the lithium metal of ananode contacts a solid-state Li⁺ conductor containing cation componentsdifferent from lithium ion, the lithium reduces the cation specie to alower oxidation state and deteriorates the solid-state conductor.

Thus, many current conventionally known solid Li-ion conductors suffer astability issue when in contact with a Li metal anode.

The inventors of this application have been studying lithium compoundswhich may serve for future use of solid-state Li+ conductors andprevious results of this study are disclosed in U.S. application Ser.No. 15/626,696, filed Jun. 19, 2017, U.S. Ser. No. 15/805,672, filedNov. 7, 2017, U.S. application Ser. No. 16/013,495, filed Jun. 20, 2018,U.S. application Ser. No. 16/114,946 filed Aug. 28, 2018, U.S.application Ser. No. 16/142,217 filed Sep. 26, 2018, U.S. applicationSer. No. 16/144,157 filed Sep. 27, 2018, U.S. application Ser. No.16/153,335 filed Oct. 10, 2018, U.S. application Ser. No. 16/155,349filed Oct. 9, 2018, U.S. application Ser. No. 16/264,294, filed Jan. 31,2019. U.S. application Ser. No. 16/570,811, filed Sep. 13, 2019, andU.S. application Ser. No. 16/570,888, filed Sep. 13, 2019. However,research effort continues to discover additional materials havingmaximum efficiency, high stability, low cost and ease of handling andmanufacture.

Accordingly, an object of this application is to identify a range offurther materials having high Li ion conductivity while being poorelectron conductors which are suitable as a solid state electrolytesand/or electrode components for lithium ion and lithium metal battery.

A further object of this application is to provide a solid state lithiumion and/or lithium metal batteries containing these materials havinghigh Li ion conductivity while being poor electron conductors.

SUMMARY OF THE EMBODIMENTS

These and other objects are provided by the embodiments of the presentapplication, the first embodiment of which includes a solid-statelithium ion electrolyte, comprising: at least one material selected fromthe group of materials consisting of compounds of formulae (I), (II),(III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I)

wherein

M is Al, Zn or a combination of Al and Zn

y is a number from greater than 0 to less than 2, x is a value such thatcharge neutrality of the formula is obtained, and M1 is at least oneelement different from Li selected from elements of groups 1, 2 and 13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II)

wherein

M is Al, Zn or a combination of Al and Zn,

z is a number from greater than 0 to less than 1, x is a value such thatthe formula (II) is charge neutral, and M2 is at least one elementdifferent from M selected from elements of groups 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)M Cl_(4-h)(X)_(h)  (III)wherein

M is Al, Zn or a combination of Al and Zn,

h is from greater than 0 to less than 4, x is a value such that theformula (III) is charge neutral, and X is at least one element differentfrom Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV)

wherein

M is Al, Zn or a combination of Al and Zn,

m is a number from 0 to less than 2, n is a number from 0 to less than1, o is a number from 0 to less than 4 and x is a value such thatformula (IV) is charge neutral, with the proviso that at least two of m,n and o cannot be 0,

wherein the compounds of formulae (I), (II), (III) and (IV) comprise acrystal lattice structure having a monoclinic phase of the space groupP2₁/c, and

with the proviso that the content of M1, M2 and/or X is a value suchthat the P2₁/c structure of the compound is maintained.

In an aspect of the first embodiment a lithium ion (Li⁺) conductivity ofthe solid state lithium ion electrolyte of formulae (I) to (IV) is from0.1 to 3 mS/cm at 300K.

In another aspect of the first embodiment an activation energy of thecomposite of formulae (I) to (IV) is from 0.15 to 0.40 eV.

In a second embodiment, a solid-state lithium battery is provided. Thebattery comprises:

an anode;

a cathode; and

a solid state lithium ion electrolyte located between the anode and thecathode;

wherein

the solid state lithium ion electrolyte comprises at least one materialselected from the group of materials consisting compounds of formulae(I), (II), (III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I)

wherein

M is Al, Zn or a combination of Al and Zn

y is a number from greater than 0 to less than 2, x is a value such thatcharge neutrality of the formula is obtained, and M1 is at least oneelement different from Li selected from elements of groups 1, 2 and 13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II)

wherein

M is Al, Zn or a combination of Al and Zn,

z is a number from greater than 0 to less than 1, x is a value such thatthe formula (II) is charge neutral, and M2 is at least one elementdifferent from M selected from elements of groups 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III)wherein

M is Al, Zn or a combination of Al and Zn,

h is from greater than 0 to less than 4, x is a value such that theformula (III) is charge neutral, and X is at least one element differentfrom Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV)

wherein

M is Al, Zn or a combination of Al and Zn,

m is a number from 0 to less than 2, n is a number from 0 to less than1, o is a number from 0 to less than 4 and x is a value such thatformula (IV) is charge neutral, with the proviso that at least two of m,n and o cannot be 0,

wherein the compounds of formulae (I), (II), (III) and (IV) comprise acrystal lattice structure having a monoclinic phase of the space groupP2₁/c, and

with the proviso that the content of M1, M2 and/or X is a value suchthat the P2₁/c structure of the compound is maintained.

The lithium battery of the second embodiment may be a lithium metalbattery or a lithium ion battery.

In a third embodiment, an electrode for a solid state lithium battery isprovided. The electrode comprises:

a current collector; and

an electrode active layer on the current collector;

wherein the electrode active layer comprises at least one compoundselected from the group consisting of compounds of formulae (I), (II),(III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I)

wherein

M is Al, Zn or a combination of Al and Zn

y is a number from greater than 0 to less than 2, x is a value such thatcharge neutrality of the formula is obtained, and M1 is at least oneelement different from Li selected from elements of groups 1, 2 and 13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II)

wherein

M is Al, Zn or a combination of Al and Zn,

z is a number from greater than 0 to less than 1, x is a value such thatthe formula (II) is charge neutral, and M2 is at least one elementdifferent from M selected from elements of groups 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III)wherein

M is Al, Zn or a combination of Al and Zn,

h is from greater than 0 to less than 4, x is a value such that theformula (III) is charge neutral, and X is at least one element differentfrom Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV)

wherein

M is Al, Zn or a combination of Al and Zn,

m is a number from 0 to less than 2, n is a number from 0 to less than1, o is a number from 0 to less than 4 and x is a value such thatformula (IV) is charge neutral, with the proviso that at least two of m,n and o cannot be 0,

wherein the compounds of formulae (I), (II), (III) and (IV) comprise acrystal lattice structure having a monoclinic phase of the space groupP2₁/c, and

with the proviso that the content of M1, M2 and/or X is a value suchthat the P2₁/c structure of the compound is maintained.

In a fourth embodiment, an electrode for a solid state lithium batteryis provided. The electrode comprises:

a current collector;

an electrode active layer on the current collector; and a coating layeron the electrode active layer;

wherein the coating layer on the electrode active layer comprises atleast one compound selected from the group consisting of compounds offormulae (I), (II), (III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I)

wherein

M is Al, Zn or a combination of Al and Zn

y is a number from greater than 0 to less than 2, x is a value such thatcharge neutrality of the formula is obtained, and M1 is at least oneelement different from Li selected from elements of groups 1, 2 and 13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II)

wherein

M is Al, Zn or a combination of Al and Zn,

z is a number from greater than 0 to less than 1, x is a value such thatthe formula (II) is charge neutral, and M2 is at least one elementdifferent from M selected from elements of groups 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III)wherein

M is Al, Zn or a combination of Al and Zn,

h is from greater than 0 to less than 4, x is a value such that theformula (III) is charge neutral, and X is at least one element differentfrom Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV)

wherein

M is Al, Zn or a combination of Al and Zn,

m is a number from 0 to less than 2, n is a number from 0 to less than1, o is a number from 0 to less than 4 and x is a value such thatformula (IV) is charge neutral, with the proviso that at least two of m,n and o cannot be 0,

wherein the compounds of formulae (I), (II), (III) and (IV) comprise acrystal lattice structure having a monoclinic phase of the space groupP2₁/c, and

with the proviso that the content of M1, M2 and/or X is a value suchthat the P2₁/c structure of the compound is maintained.

Solid state lithium batteries containing the electrodes and/orelectrolytes of the various embodiments and aspects thereof are alsoprovided. The solid state lithium battery may be a lithium metal batteryor a lithium ion battery.

The foregoing description is intended to provide a general introductionand summary of the present disclosure and is not intended to be limitingin its disclosure unless otherwise explicitly stated. The presentlypreferred embodiments, together with further advantages, will be bestunderstood by reference to the following detailed description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 shows the crystal structure of Li₂ZnCl₄ of the P2₁/c space group.

FIG. 2 shows the XRD analysis of the crystal structure of Li₂ZnCl₄ ofthe P2₁/c space group.

FIG. 3 shows a table listing the peak positions and intensity for peaksof relative intensity of 1 or greater compared to the peak of greatestintensity in the XRD analysis of Li₂ZnCl₄ in FIG. 2 .

FIG. 4 shows the crystal structure of Li_(1.5)Zn_(0.5)Al_(0.5)Cl₄ of thePmn2₁ space group.

FIG. 5 shows the XRD analysis of the crystal structure ofLi_(1.5)Zn_(0.5)Al_(0.5)Cl₄ of the P2₁/c space group.

FIG. 6 shows a table listing the peak positions and intensity for peaksof relative intensity of 1 or greater compared to the peak of greatestintensity in the XRD analysis of Li_(1.5)Zn_(0.5)Al_(0.5)Cl₄ in FIG. 5 .

FIG. 7 shows the crystal structure of Li_(1.25)Al_(0.75)Zn_(0.25)Cl₄ ofthe P2₁/c P2₁/c space group.

FIG. 8 shows the XRD analysis of the crystal structure ofLi_(1.25)Al_(0.75)Zn_(0.25)Cl₄ of the P2₁/c space group.

FIG. 9 shows a table listing the peak positions and intensity for peaksof relative intensity of 1 or greater compared to the peak of greatestintensity in the XRD analysis of Li_(1.25)Al_(0.75)Zn_(0.25)Cl₄ in FIG.8 .

FIG. 10 shows the crystal structure of LiAlCl₄.

FIG. 11 shows an Arrhenius plot of Li-ion diffusivity D in LiZnCl₄obtained from AIMD simulations.

FIG. 12 shows the Li-ion probability density in Li₂ZnCl₄ obtained fromAIMD simulations.

FIG. 13 shows the Li-ion probability density inLi_(1.5)Zn_(0.5)Al_(0.5)Cl₄ obtained from AIMD simulations.

FIG. 14 shows the Li-ion probability density inLi_(1.25)Al_(0.75)Zn_(0.25)Cl₄ obtained from AIMD simulations.

FIG. 15 shows the Li-ion probability density in LiAlCl₄ obtained fromAIMD simulations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout this description, the terms “electrochemical cell” and“battery” may be employed interchangeably unless the context of thedescription clearly distinguishes an electrochemical cell from abattery. Further the terms “solid-state electrolyte” and “solid-stateion conductor” may be employed interchangeably unless explicitlyspecified differently.

Structural characteristics of effective Li⁺ conducting crystal latticeshave been described by Ceder et al. (Nature Materials, 14, 2015,1026-1031) in regard to known Li⁺ ion conductors Li₁₀GeP₂S₁₂ andLi₇P₃S₁₁, where the sulfur sublattice of both materials was shown tovery closely match a bcc lattice structure. Further, Li⁺ ion hoppingacross adjacent tetrahedral coordinated Li⁺ lattice sites was indicatedto offer a path of lowest activation energy.

The inventors are conducting ongoing investigations of new lithiumcomposite compounds in order to identify materials having the propertieswhich may serve as solid-state electrolytes in solid state lithiumbatteries. In the course of this ongoing study and effort the inventorshave developed and implemented a methodology to identify compositematerials which have chemical and structural properties which have beendetermined by the inventors as indicators of lithium ion conductancesuitable to be a solid state electrolyte for a lithium-ion battery andcomponents of an electrode adjacent to the solid state electrolyte.

To qualify as solid state electrolyte in practical applications, thematerial must meet several certain criteria. First, it should exhibitdesirable Li-ion conductivity, usually no less than 10⁻⁶ S/cm at roomtemperature. Second, the material should have good stability againstchemical, electrochemical and thermal degradation. Third, the materialshould have low grain boundary resistance for usage in all solid-statebattery. Fourth, the synthesis of the material should be easy and thecost should not be high.

A criterion of this methodology requires that to qualify as solid stateelectrolyte in practical application, the material must exhibitdesirable Li-ion conductivity, usually no less than 10⁻⁶ S/cm at roomtemperature. Thus, ab initio molecular dynamics simulation studies wereapplied to calculate the diffusivity of Li ion in the lattice structuresof selected silicate materials. In order to accelerate the simulation,the calculation was performed at high temperatures and the effect ofexcess Li or Li vacancy was considered. In order to create excess Li orLi vacancy, aliovalent replacement of cation or anions may be evaluated.Thus, Li vacancy was created by, for example, partially substituting Siwith aliovalent cationic species while compensating the chargeneutrality with Li vacancy or excess Li. For example, replacing 50% ofSi in Li₁₀Si₂PbO₁₀ with P results in the formation of Li₉PSiPbO₁₀.

The diffusivity at 300 K was determined according to equation (I)D=D ₀ exp(−E _(a) /k _(b) T)  equation (I)where D₀, E_(a) and k_(b) are the pre-exponential factor, activationenergy and Boltzmann constant, respectively. The conductivity is relatedwith the calculated diffusivity according to equation (II):σ=D ₃₀₀ ρe ² /k _(b) T  equation (II)where ρ is the volumetric density of Li ion and e is the unit charge.

The anionic lattice of Li-ion conductors has been shown to match certainlattice types (see Nature Materials, 14, 2015, 2016). Therefore, in theanionic lattice of the potential Li⁺ ion conductor is compared to theanionic lattice of Li⁺ ion conductor known to have high conductivity.

Thus, selected metal lithium chloride derivative compounds were comparedto Li-containing compounds reported in the inorganic crystal structuredatabase (FIZ Karlsruhe ICSD—https://icsd.fiz-karlsruhe.de) andevaluated in comparison according to an anionic lattice matching methoddeveloped by the inventors for this purpose and described in copendingU.S. application Ser. No. 15/597,651, filed May 17, 2017, to match thelattice of these compounds to known Li-ion conductors.

According to the anionic lattice matching method described in copendingU.S. application Ser. No. 15/597,651, an atomic coordinate set for thecompound lattice structure may be converted to a coordinate set for onlythe anion lattice. The anions of the lattice are substituted with theanion of the comparison material and the obtained unit cell rescaled.The x-ray diffraction data for modified anion-only lattice may besimulated and an n×2 matrix generated from the simulated diffractiondata. Quantitative structural similarity values can be derived from then×2 matrices.

The purpose of anionic lattice matching is to further identify compoundswith greatest potential to exhibit high Li⁺ conductivity. From thiswork, the compounds described in the embodiments which follow weredetermined to be potentially suitable as a solid-state Li⁺ conductors.

Ab initio molecular dynamics (AIMD) simulation was then applied topredict the conductivity of the targeted lithium aluminum chloridederivative compounds. The initial structures were statically relaxed andwere set to an initial temperature of 100 K. The structures were thenheated to targeted temperatures (550-650 K) at a constant rate byvelocity scaling over a time period of 2 ps. The total time of AIMDsimulations were in the range of 400 to 1000 ps. A typical example ofthe calculated diffusivity as a function of temperature is shown in FIG.11 . The Li⁺ diffusivity at different temperatures from 500-650 Kfollows an Arrhenius-type relationship.

Applying equation (I) above the diffusivity at 300 K was determined andthen the conductivity may be determined using the link betweenconductivity and diffusivity of equation (II).

Accordingly, the first embodiment provides a solid-state lithium ionelectrolyte, comprising: at least one material selected from the groupof materials consisting of compounds of formulae (I), (II), (III) and(IV):Li_(x-y)(M1)_(y)MCl₄  (I)

wherein

M is Al, Zn or a combination of Al and Zn

y is a number from greater than 0 to less than 2, x is a value such thatcharge neutrality of the formula is obtained, and M1 is at least oneelement different from Li selected from elements of groups 1, 2 and 13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II)

wherein

M is Al, Zn or a combination of Al and Zn,

z is a number from greater than 0 to less than 1, x is a value such thatthe formula (II) is charge neutral, and M2 is at least one elementdifferent from M selected from elements of groups 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III)wherein

M is Al, Zn or a combination of Al and Zn,

h is from greater than 0 to less than 4, x is a value such that theformula (III) is charge neutral, and X is at least one element differentfrom Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV)

wherein

M is Al, Zn or a combination of Al and Zn,

m is a number from 0 to less than 2, n is a number from 0 to less than1, o is a number from 0 to less than 4 and x is a value such thatformula (IV) is charge neutral, with the proviso that at least two of m,n and o cannot be 0,

wherein the compounds of formulae (I), (II), (III) and (IV) comprise acrystal lattice structure having a monoclinic phase of the space groupP2₁/c, and

with the proviso that the content of M1, M2 and/or X is a value suchthat the P2₁/c structure of the compound is maintained.

The compounds of formulae (I)-(IV) are derivative compounds of Li₂ZnCl₄or LiAlCl₄ having a crystal lattice structure of a monoclinic phase ofthe space group P2₁/c. The crystal lattice structure of the Li₂ZnCl₄ ofthe P2₁/c space group is depicted in FIG. 1 and a calculated X-raydiffraction (XRD) pattern based on Cu-Kα radiation with wavelength of1.54184 Å for this space group is shown in FIG. 2 . The peak positionsand relative intensities are shown in FIG. 3 .

The inventors have determined that substitution of elements M1 for Li,M2 for Zn and/or Al and X for Cl in the Li₂ZnCl₄ or LiAlCl₄ of P2₁/cspace group may enhance Li ion mobility and increase Li ion densitywithin the crystal lattice to provide efficient Li ion conductors usefulas solid electrolytes for lithium batteries.

The degree of doping or substitution that can be made and still retainthe P2₁/c morphology varies with the element being employed as dopant.Generally, the more similar in ionic radius and electronic structure thegreater the mole amount of dopant that can be used without significantchange of crystal morphology. The simulation methods applied anddescribed herein may be employed to determine the degree of doping witha given element that can be made without changing the basic P2₁/ccrystal structure.

In further aspects of the first embodiment the simulation study hasdetermined that the solid state electrolytes of formulae (I) to (IV) mayhave a lithium ion (Li⁺) conductivity of from 0.01 to 3 mS/cm preferably0.1 to 3 mS/cm at 300K.

Moreover, the activation energy of the solid state electrolytes offormulae (I) to (IV) may be from 0.15 to 0.40 eV.

Synthesis of the composite materials of the embodiments described abovemay be achieved by solid state reaction between stoichiometric amountsof selected precursor materials. Exemplary methods of solid statesynthesis are described for example in each of the following papers: i)Monatshefte für Chemie, 100, 295-303, 1969; ii) Journal of Solid StateChemistry, 128, 1997, 241; iii) Zeitschrift für Naturforschung B, 50,1995, 1061; iv) Journal of Solid State Chemistry 130, 1997, 90; v)Journal of Alloys and Compounds, 645, 2015, S174; and vi) Z.Naturforsch. 51b, 1996525.

In further embodiments, the present application includes solid statelithium ion batteries containing the solid-state electrolytes describedabove. Solid-state batteries of these embodiments including metal-metalsolid-state batteries may have higher charge/discharge rate capabilityand higher power density than classical batteries and may have thepotential to provide high power and energy density.

Thus, in further embodiments, solid-state lithium batteries areprovided. The solid state lithium battery comprises: an anode; acathode; and a solid state lithium ion electrolyte located between theanode and the cathode; wherein

the solid state lithium ion electrolyte comprises at least one materialselected from the group of materials consisting compounds of formulae(I), (II), (III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I)

wherein

M is Al, Zn or a combination of Al and Zn

y is a number from greater than 0 to less than 2, x is a value such thatcharge neutrality of the formula is obtained, and M1 is at least oneelement different from Li selected from elements of groups 1, 2 and 13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II)

wherein

M is Al, Zn or a combination of Al and Zn,

z is a number from greater than 0 to less than 1, x is a value such thatthe formula (II) is charge neutral, and M2 is at least one elementdifferent from M selected from elements of groups 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III)wherein

M is Al, Zn or a combination of Al and Zn,

h is from greater than 0 to less than 4, x is a value such that theformula (III) is charge neutral, and X is at least one element differentfrom Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV)

wherein

M is Al, Zn or a combination of Al and Zn,

m is a number from 0 to less than 2, n is a number from 0 to less than1, o is a number from 0 to less than 4 and x is a value such thatformula (IV) is charge neutral, with the proviso that at least two of m,n and o cannot be 0,

wherein the compounds of formulae (I), (II), (III) and (IV) comprise acrystal lattice structure having a monoclinic phase of the space groupP2₁/c, and

with the proviso that the content of M1, M2 and/or X is a value suchthat the P2₁/c structure of the compound is maintained.

The anode may be any anode structure conventionally employed in alithium ion battery. Generally such materials are capable of insertionand extraction of Li⁺ ions. Example anode active materials may includegraphite, hard carbon, lithium titanate (LTO), a tin/cobalt alloy andsilicon/carbon composites. In one aspect the anode may comprise acurrent collector and a coating of a lithium ion active material on thecurrent collector. Standard current collector materials include but arenot limited to aluminum, copper, nickel, stainless steel, carbon, carbonpaper and carbon cloth. In an aspect advantageously arranged with thesolid-state lithium ion conductive materials described in the first andsecond embodiments, the anode may be lithium metal or a lithium metalalloy, optionally coated on a current collector. In one aspect, theanode may be a sheet of lithium metal serving both as active materialand current collector.

The cathode structure may be any conventionally employed in lithium ionbatteries, including but not limited to composite lithium metal oxidessuch as, for example, lithium cobalt oxide (LiCoO₂), lithium manganeseoxide (LiMn₂O₄), lithium iron phosphate (LiFePO₄) and lithium nickelmanganese cobalt oxide. Other active cathode materials may also includeelemental sulfur and metal sulfide composites. The cathode may alsoinclude a current collector such as copper, aluminum and stainlesssteel.

In one aspect, the active cathode material may be a transition metal,preferably, silver or copper. A cathode based on such transition metalmay not include a current collector.

In a further set of embodiments, electrodes containing the solidelectrolyte materials of formulae (I)-(IV) are also disclosed. Thus inthe preparation of the electrode the active material as described abovemay be physically mixed with the solid electrolyte material beforeapplication to the current collector or the solid electrolyte materialmay be applied as a coating layer on the applied active material. Ineither embodiment the presence of the lithium ion super conductor on orwithin the the electrode structure may enhance performance of theelectrode and especially when applied as a coating layer, may serve toprotect a conventional solid state electrolyte.

Thus, an embodiment of the present disclosure includes a cathodecomprising a current collector and a layer of cathode active materialapplied to the current collector wherein at least one of the followingcomponents is present: i) the cathode active material applied to thecurrent collector is a physical mixture containing at least one of thesolid electrolyte materials of formulae (I)-(IV) as described above; andii) the layer of cathode active material applied to the currentcollector is coated with a layer comprising at least one of the solidelectrolyte materials of formulae (I)-(IV). Cathodes having bothelements i) and ii) are also included in the present disclosure.

In related embodiments the present disclosure includes an anodecomprising a current collector and a layer of anode active materialapplied to the current collector wherein at least one of the followingcomponents is present: i) the anode active material applied to thecurrent collector is a physical mixture containing at least one of thesolid electrolyte materials of formulae (I)-(IV) as described above; andii) the layer of anode active material applied to the current collectoris coated with a layer comprising at least one of the solid electrolytematerials of formulae (I)-(IV).

Batteries containing a cathode as described in the above embodiment, ananode described in the above embodiment or containing both an anode andcathode according to the above embodiments are also embodiments of thepresent disclosure.

EXAMPLES

Compounds of the formule Li_(1.5)Zn_(0.5)Al_(0.5)Cl₄ andLi_(1.25)Al_(0.75)Zn_(0.25)Cl₄ in the space group P2₁/c were studiedemploying the ab initio dynamics simulation to determine the conductionproperties of these compounds and their derivatives. The initialstructures were statically relaxed and were set to an initialtemperature of 100 K. The structures were then heated to targetedtemperatures (500-650 K) at a constant rate by velocity scaling over atime period of 2 ps. The total time of AIMD simulations were in therange of 400 to 1000 ps. The Li⁺ diffusivity at different temperaturesfrom 500-650 K follows an Arrhenius-type relationship

Both compounds are doped derivatives of Li₂ZnCl₄ and/or LiAlCl₄ having amonoclinic space group P2₁/c lattice structure. The crystal structure ofP2₁/c Li₂ZnCl₄ is shown in FIG. 1 . FIG. 2 shows the XRD analysis of thecrystal structure of the P2₁/c Li₂ZnCl₄ and FIG. 3 shows a table listingthe peak positions and intensity for peaks of relative intensity of 1 orgreater compared to the peak of greatest intensity in the XRD analysisof FIG. 2 . FIG. 10 shows the Arrhenius plot of Li-ion diffusivity Dwith temperature for P2₁/c Li₂ZnCl₄.

The Energy above the hull and Li-ion conductivity at 500 K of Li₂ZnCl₄,the substituted compounds and LiAlCl₄ from AIMD simulations is shown inthe following Table.

E_(hull) Composition (meV/atom) σ (mS/cm) at 500K Li₂ZnCl₄ 19 135Li_(1.5)Al_(0.5)Zn_(0.5)Cl₄ 26 259 Li_(1.25)Al_(0.75)Zn_(0.25)Cl₄ 11 226LiAlCl₄ 0 235

The activation energy of Li₂ZnCl₄ is 0.33±0.06 eV, the Li-ionconductivity at 300 K of Li₂ZnCl₄ is 2.6 mS cm⁻¹ with error bounds [0.2mS cm⁻¹, 37.5 mS cm⁻¹], the energy above the hull E_(hull) is 19 meV peratom, and the electrochemical window of Li₃InCl₆ is 1.91 to 4.21 Vreferred to Li/Li⁺. The energy above the hull is the energy differencebetween the compound and its stable phase equilibria, which isconventionally used as a descriptor to justify the metastability andsynthesizability of a compound. The E_(hull) of Li₂ZnCl₄ (12 meV/atom)is lower than 30 meV/atom which implies experimental synthesizability(see A. H. Nolan, Y. Zhu, X. He, Q. Bai, Y. Mo, Joule 2018, 22016.)

FIG. 4 shows the crystal structure of Li_(1.5)Zn_(0.5)Al_(0.5)Cl₄ in theP2₁/c space group. FIG. 5 shows the XRD analysis of the crystalstructure of P2₁/c Li_(1.5)Zn_(0.5)Al_(0.5)Cl₄ and FIG. 6 shows a tablelisting the peak positions and intensity for peaks of relative intensityof 1 or greater compared to the peak of greatest intensity in the XRDanalysis of FIG. 5 .

FIG. 7 shows the crystal structure of P2₁/cLi_(1.25)Al_(0.75)Zn_(0.25)Cl₄. FIG. 8 shows the XRD analysis of thecrystal structure of Li_(1.75)Zn_(0.75)Al_(0.25)Cl₄ in the P2₁/c spacegroup and FIG. 9 shows a table listing the peak positions and intensityfor peaks of relative intensity of 1 or greater compared to the peak ofgreatest intensity in the XRD analysis of FIG. 8 .

FIG. 10 shows the crystal structure for monoclinic P2₁/c LiAlCl₄.

FIGS. 12, 13, 14 and 15 show the Li-ion probability density in Li₂ZnCl₄,Li_(1.5)Zn_(0.5)Al_(0.5)Cl₄, Li_(1.25)Al_(0.75)Zn_(0.25)Cl₄ and LiAlCl₄of space group P2₁/c respectively obtained from AIMD simulations. TheLi-ion probability density extracted from AIMD simulations counts thefraction of Li-ion in each spatial location in the crystal structures.(see He. X, Zhu, y. and Mo, Y. Nat Commun 8, 15893 (2017)). The Li-ionprobability densities in FIGS. 12 to 15 show good channels for Li-ionconduction in the crystal structure. The high probability of Li-ionhopping for the doped materials of P2₁/c Li₂ZnCl₄ and LiAlCl₄demonstrates the advantageous lithium ion conductivity obtained with thecompounds of formulae (I)-(IV).

Thus, these materials having the crystal morphology of the P2₁/c spacegroup have the excellent properties necessary to function as a highLi-ion conductive solid electrolyte, a protective coating for anelectrode or an active component of an electrode.

The above description is presented to enable a person skilled in the artto make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein. In thisregard, certain embodiments within the invention may not show everybenefit of the invention, considered broadly.

The invention claimed is:
 1. A solid-state lithium ion electrolyte,comprising: at least one material selected from the group of materialsconsisting of compounds of formulae (I), (II) (III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I) wherein M is Al, Zn or a combination of Al andZn y is a number from greater than 0 to less than 2, x is a value suchthat charge neutrality of the formula is obtained, and M1 is at leastone element different from Li selected from elements of groups 1, 2 and13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II) wherein M is Al, Zn or a combination ofAl and Zn, z is a number from greater than 0 to less than 1, x is avalue such that the formula (II) is charge neutral, and M2 is at leastone element different from M selected from elements of groups 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)M Cl_(4-h)(X)_(h)  (III) wherein M is Al, Zn or a combination ofAl and Zn, h is from greater than 0 to less than 4, x is a value suchthat the formula (III) is charge neutral, and X is at least one elementdifferent from Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV) wherein M is Al, Znor a combination of Al and Zn, m is a number from 0 to less than 2, n isa number from 0 to less than 1, o is a number from 0 to less than 4 andx is a value such that formula (IV) is charge neutral, with the provisothat at least two of m, n and o cannot be 0, wherein the compounds offormulae (I), (II), (III) and (IV) have a crystal lattice structure of amonoclinic phase of the space group P2₁/c, and with the proviso that thecontent of M1, M2 and/or X is a value such that the P2₁/c structure ofthe compound is maintained.
 2. The solid state lithium ion electrolyteaccording to claim 1, wherein a lithium ion (Li⁺) conductivity of thesolid state lithium ion electrolyte is from 0.1 to 3 mS/cm at 300K. 3.The solid state lithium ion electrolyte according to claim 1, wherein anactivation energy of the material is from 0.15 to 0.40 eV.
 4. The solidstate electrolyte according to claim 1 wherein a calculated XRD analysisbased on Cu-Kα radiation with wavelength of 1.54184 Å comprises thefollowing peaks defining the P2₁/c space group: Peak Position RelativeIntensity 13.197 19.81 13.880 20.53 17.057 79.89 17.059 69.46 17.58455.14 17.605 56.84 19.022 54.55 21.616 29.39 22.200 36.55 22.219 39.5725.408 53.96 25.411 46.95 25.765 23.02 25.794 23.73 26.573 79.75 27.969100.0 29.169 20.77 29.198 23.27 29.869 20.65 31.828 11.67 31.839 11.9437.536 11.54 37.561 11.24 38.248 15.57 38.282 12.85 38.307 26.87 38.35024.17 38.596 32.34 44.053 46.02 46.209 37.28 46.214 37.10 48.147 14.9148.199 15.36 50.371 11.24 50.389 11.53 50.423 11.53 52.962 11.59 53.02711.62 55.288 10.71 55.324 10.73


5. A solid state lithium battery, comprising: an anode; a cathode; and asolid state lithium ion electrolyte located between the anode and thecathode; wherein the solid state lithium ion electrolyte comprises atleast one material selected from the group of materials consistingcompounds of formulae (I), (II), (III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I) wherein M is Al, Zn or a combination of Al andZn y is a number from greater than 0 to less than 2, x is a value suchthat charge neutrality of the formula is obtained, and M1 is at leastone element different from Li selected from elements of groups 1, 2 and13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II) wherein M is Al, Zn or a combination ofAl and Zn, z is a number from greater than 0 to less than 1, x is avalue such that the formula (II) is charge neutral, and M2 is at leastone element different from M selected from elements of groups 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III) wherein M is Al, Zn or a combination of Aland Zn, h is from greater than 0 to less than 4, x is a value such thatthe formula (III) is charge neutral, and X is at least one elementdifferent from Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV) wherein M is Al, Znor a combination of Al and Zn, m is a number from 0 to less than 2, n isa number from 0 to less than 1, o is a number from 0 to less than 4 andx is a value such that formula (IV) is charge neutral, with the provisothat at least two of m, n and o cannot be 0, wherein the compounds offormulae (I), (II), (III) and (IV) have a crystal lattice structurehaving a monoclinic phase of the space group P2₁/c, and with the provisothat the content of M1, M2 and/or X is a value such that the P2₁/cstructure of the compound is maintained.
 6. The solid state lithium ionbattery according to claim 5, wherein the battery is a lithium metalbattery or a lithium ion battery.
 7. An electrode for a solid statelithium battery, comprising: a current collector; and an electrodeactive layer on the current collector; wherein the electrode activelayer comprises at least one compound selected from the group consistingof compounds of formulae (I), (II), (III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I) wherein M is Al, Zn or a combination of Al andZn y is a number from greater than 0 to less than 2, x is a value suchthat charge neutrality of the formula is obtained, and M1 is at leastone element different from Li selected from elements of groups 1, 2 and13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II) wherein M is Al, Zn or a combination ofAl and Zn, z is a number from greater than 0 to less than 1, x is avalue such that the formula (II) is charge neutral, and M2 is at leastone element different from M selected from elements of groups 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III) wherein M is Al, Zn or a combination of Aland Zn, h is from greater than 0 to less than 4, x is a value such thatthe formula (III) is charge neutral, and X is at least one elementdifferent from Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV) wherein M is Al, Znor a combination of Al and Zn, m is a number from 0 to less than 2, n isa number from 0 to less than 1, o is a number from 0 to less than 4 andx is a value such that formula (IV) is charge neutral, with the provisothat at least two of m, n and o cannot be 0, wherein the compounds offormulae (I), (II), (III) and (IV) have a crystal lattice structurehaving a monoclinic phase of the space group P2₁/c, and with the provisothat the content of M1, M2 and/or X is a value such that the P2₁/cstructure of the compound is maintained.
 8. An electrode for a solidstate lithium battery, comprising: a current collector; an electrodeactive layer on the current collector; and a coating layer on theelectrode active laver; wherein the coating layer on the electrodeactive layer comprises at least one compound selected from the groupconsisting of compounds of formulae (I), (II), (III) and (IV):Li_(x-y)(M1)_(y)MCl₄  (I) wherein M is Al, Zn or a combination of Al andZn y is a number from greater than 0 to less than 2, x is a value suchthat charge neutrality of the formula is obtained, and M1 is at leastone element different from Li selected from elements of groups 1, 2 and13;Li_(x)M_(1-z)(M2)_(z)Cl₄  (II) wherein M is Al, Zn or a combination ofAl and Zn, z is a number from greater than 0 to less than 1, x is avalue such that the formula (II) is charge neutral, and M2 is at leastone element different from M selected from elements of groups 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16 and 17; andLi_(x)MCl_(4-h)(X)_(h)  (III) wherein M is Al, Zn or a combination of Aland Zn, h is from greater than 0 to less than 4, x is a value such thatthe formula (III) is charge neutral, and X is at least one elementdifferent from Cl selected from elements of groups 16 and 17; andLi_(x-m)(M1)_(m)M_(1-n)(M2)_(n)Cl_(4-o)(X)_(o)  (IV) wherein M is Al, Znor a combination of Al and Zn, m is a number from 0 to less than 2, n isa number from 0 to less than 1, o is a number from 0 to less than 4 andx is a value such that formula (IV) is charge neutral, with the provisothat at least two of m, n and o cannot be 0, wherein the compounds offormulae (I), (II), (III) and (IV) have a crystal lattice structurehaving a monoclinic phase of the space group P2₁/c, and with the provisothat the content of M1, M2 and/or X is a value such that the P2₁/cstructure of the compound is maintained.
 9. A solid state lithiumbattery comprising the electrode of claim 7, wherein the solid statelithium battery is a lithium ion battery or a lithium metal battery. 10.A solid state lithium battery comprising the electrode of claim 8,wherein the solid state lithium battery is a lithium ion battery or alithium metal battery.